1. Technical Field
The present invention relates to an optical filter, an optical filter module, a spectrometric measurement apparatus, an optical apparatus, and other apparatus.
2. Related Art
An interference filter has been used in a spectrometric measurement apparatus and other optical apparatus. A known aspect of an interference filter selects the wavelength of light that passes therethrough (Fabry-Perot etalon interference filter) (see JP-A-11-142752, for example). The transmissive variable wavelength interference filter described in JP-A-11-142752, which can select the wavelength of light passing therethrough, includes a pair of substrates held in parallel to each other and a pair of multilayer films (optical films) so formed on the pair of substrates that the multilayer films (optical films) face each other and have a fixed-distance gap therebetween. The interference filter selects the wavelength of light passing therethrough by using an external force to change the size of the gap (interference gap) between the pair of multilayer films (optical films).
When a single variable wavelength filter (variable gap etalon filter, for example) is used to cover a desired wavelength band and perform n-point spectrometric measurement (n is an integer greater than or equal to two), the size of the gap between the multilayer films (optical films) in the variable wavelength filter needs to be changed. Specifically, it is necessary to repeat the following actions multiple times corresponding to the number of measurement points: changing the size of the gap to provide a spectral band corresponding to each of the measurement points and then performing spectrometric measurement in the spectral band. A wide bandwidth of the desired wavelength band therefore increases the measurement period required to acquire all necessary measured data. That is, it disadvantageously takes a long time for the variable wavelength filter to scan the entire desired wavelength band.